[mythtv-users] remaining disk space / delete slowly

[Karl Newman]

On Tue, Jul 12, 2016 at 6:37 PM, James Linder <jam at tigger.ws> wrote:

>
> > On 12 Jul 2016, at 8:00 PM, mythtv-users-request at mythtv.org wrote:
> >
> > No, the slow deletes are simply to allow MythTV to spread the I/O
> > requirements for deleting a file (generally a very large, multi-gigabyte
> > file) over a long period of time (IIRC, about 2min/GB) rather than
> > telling the OS to delete the entire, huge file and letting it force all
> > that I/O to occur "immediately". Therefore, if your system has other I/O
> > requirements (such as, for example, writing out recording files for new
> > recordings that are currently in progress, or writing information to
> > your MySQL database (eg, about in-progress recordings), or reading
> > information from your MySQL database (eg, to refresh the information
> > about your existing/remaining recordings), that (much, much)
> > higher-priority I/O can occur without having to wait on the unimportant,
> > low-priority I/O associated with deleting a recording.  This can be very
> > important when deleting a bunch of huge files because it's possible for
> > the new recording information to grow too large for the system to keep
> > in memory before it's written to disk at which point information  is
> > lost (and files are corrupted--including recording files and even
> > potentially your MySQL database data files).
>
> Can someone who KNOWS offer some explanation, this sounds like gibberish
>
> Mike Dean is one of the MythTV developers, and he KNOWS. It may sound like
gibberish to you, but it was a real problem with ext3 file systems. That's
why in the early days of MythTV it was recommended to use something like
JFS or XFS which deleted large files quickly. I understand it's been
mitigated somewhat with ext4.

Karl
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